Oscillatory Superconducting Transition Temperature in Nb/Gd Multilayers

Jiang, J. S.; Davidović, Dragomir; Reich, Daniel H.; Chien, C. L.

doi:10.1103/physrevlett.74.314

Cited by 397 publications

(271 citation statements)

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“…First the oscillatory behavior of T c (d F ) was observed by Wong et al 5 in V/Fe multilayers and later on these results were well explained by theoretical calculations of Radović et al 4 However, in subsequent experiments with V/Fe multilayers 6 , the oscillatory T c (d F ) dependence was not observed. The following experiments 7,8,9,10,11,12,13 revealed the different and even controversial behavior of T c (d F ) for different structures. The nonmonotonic oscillation-like behavior of T c (d F ) was reported by Jiang et al 7 for Nb/Gd multilayers and Nb/Gd/Nb trilayers, by Mühge et al 8 for Fe/Nb/Fe trilayers and recently by Obi et al 9 for Nb/Co and V/Co multilayers.…”

Section: Introductionmentioning

confidence: 99%

“…The following experiments 7,8,9,10,11,12,13 revealed the different and even controversial behavior of T c (d F ) for different structures. The nonmonotonic oscillation-like behavior of T c (d F ) was reported by Jiang et al 7 for Nb/Gd multilayers and Nb/Gd/Nb trilayers, by Mühge et al 8 for Fe/Nb/Fe trilayers and recently by Obi et al 9 for Nb/Co and V/Co multilayers. However, negative results were reported for Nb/Gd/Nb trilayers by Strunk et al 10 , for V/V 1−x Fe x multilayers by Aarts et al 11 , for Fe/Nb bilayers by Mühge et al 12 and Nb/Fe multilayers by Verbanck et al 13 .…”

Section: Introductionmentioning

confidence: 99%

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Theory of proximity effect in superconductor/ferromagnet heterostructures

2003

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We present a microscopic theory of proximity effect in the ferromagnet/superconductor-/ferromagnet (F/S/F) nanostructures where S is s-wave low-Tc superconductor and F's are layers of 3d transition ferromagnetic metal. Our approach is based on the direct analytical solution of Gor'kov equations for the normal and anomalous Green's functions together with a self-consistent evaluation of the superconducting order parameter. We take into account the elastic spin-conserving scattering of the electrons assuming s-wave scattering in the S layer and s-d scattering in the F layers. In accordance with the previous quasiclassical theories, we found that due to exchange field in the ferromagnet the anomalous Green's function F (z) exhibits the damping oscillations in the F-layer as a function of distance z from the S/F interface. In the given model a half of period of oscillations is determined by the length ξ 0 m = πvF /εex, where vF is the Fermi velocity and εex is the exchange field, while damping is governed by the length l0 = (1/l ↑ + 1/l ↓ ) −1 with l ↑ and l ↓ being spin-dependent mean free paths in the ferromagnet. The superconducting transition temperature Tc(dF ) of the F/S/F trilayer shows the damping oscillations as a function of the F-layer thickness dF with period ξF = π/ √ mεex, where m is the effective electron mass. The oscillations of Tc(dF ) are a consequence of the oscillatory behavior of the superconducting order parameter at the S/F interface vs thickness dF , that in turn is caused by the oscillations of F (z) in the F-region. We show that strong spin-conserving scattering either in the superconductor or in the ferromagnet significantly suppresses these oscillations. The calculated Tc(dF ) dependences are compared with existing experimental data for Fe/Nb/Fe trilayers and Nb/Co multilayers.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Theory of proximity effect in superconductor/ferromagnet heterostructures

2003

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“…5,6 In this state, the real part of the order parameter penetrates the ferromagnet a distance on the order of the coherence length ξ F and oscillates due to dephasing by the exchange energy of the ferromagnet. This leads to the oscillations of the superconducting transition temperature (T c ) as a function of ferromagnet thickness [7][8][9][10][11] and π phase shift in S/F junctions. 12,13 Furthermore, recent measurements in S/F structures 11,[14][15][16] have provided evidence for triplet pairing in the ferromagnet induced by noncollinear magnetizations of the F layers.…”

Section: Introductionmentioning

confidence: 99%

Vortex flipping in superconductor/ferromagnet spin-valve structures

et al. 2013

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We report in-plane magnetization measurements on Ni/Nb/Ni/CoO and Co/Nb/Co/CoO spin valve structures with one of the ferromagnetic layers pinned by an antiferromagnetic layer. In samples with Ni below the superconducting transition T c , our results show strong evidence of vortex flipping driven by ferromagnet magnetization. This is a direct consequence of the proximity effect that leads to vortex supercurrent leakage into the ferromagnets. Here, the polarized electron spins are subject to the vortices' magnetic field, occasioning vortex flipping. Such a novel mechanism has been made possible by fabrication of the ferromagnet/superconductor/ferromagnet/antiferromagnet multilayered spin valves with an S layer thin enough to barely confine vortices inside as well as F layers thin enough to align and control magnetization within the plane. When Co is used, the vortex flipping effect is not observed. This is attributed to the shorter coherence length of Co. Interestingly, a reduction in the pinning field of about 400 Oe is observed instead when the Nb layer is in the superconducting state. This effect cannot be explained in terms of vortex fields. In view of these facts, any explanation must be directly related to the proximity effect and thus a remarkable phenomenon that deserves further investigation.

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“…2 Another is the possibility of a phase difference ⌬ ϭ over an S/F/S junction, 3 resulting in an oscillatory behavior of the superconducting transition temperature T c with F-layer thickness d F of S/F multilayers. [4][5][6] An oscillation in T c was recently reported for Nb/Gd, 7 but its origin is still controversial. 8 All such effects concern the behavior of the superconducting order parameter near the S/F interface, and in that sense they form part of the general issue of the proximity effect, well known for the S/N case, but hardly investigated for the S/F case.…”

Section: Introductionmentioning

confidence: 99%

Interface transparency of superconductor/ferromagnetic multilayers

et al. 1997

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Interface transparency of superconductor/ferromagnetic multilayersAarts, J.; Geers, J.M.E.; Bruck, E.H.; Golubov, A.A.; Coehoorn, R.; Olsovec, M. General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. We have investigated the behavior of the superconducting transition temperature T c in superconducting/ ferromagnetic ͑S/F͒ multilayers, as a function of the different layer thicknesses and for varying magnetic moment F of the F-layer atoms. The system studied consists of superconducting V and ferromagnetic V 1Ϫx Fe x alloys with x such that F on the Fe atom is varied between 2 and 0.25 B . We determined the superconducting coherence length in the F layer F , which is found to be inversely proportional to F . We also determined the critical thickness of the S layer, above which superconductivity appears. This thickness is found to be strongly nonmonotonic as function of the Fe concentration in the alloys. By analyzing the data in terms of the proximity-effect theory, we show that with increasing F , the increasing pair breaking in the F layer by the exchange field is counteracted by a decreasing transparency of the S/F interface for Cooper pairs.

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Oscillatory Superconducting Transition Temperature in Nb/Gd Multilayers

Cited by 397 publications

References 16 publications

Theory of proximity effect in superconductor/ferromagnet heterostructures

Theory of proximity effect in superconductor/ferromagnet heterostructures

Vortex flipping in superconductor/ferromagnet spin-valve structures

Interface transparency of superconductor/ferromagnetic multilayers

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